The present invention relates to communications networks. More particularly, and not by way of limitation, the present invention is directed to a system and method for media gateway negotiation in a telecommunications network.
Layered network architecture is commonly used in telecommunication networks. At call setup, a Call Control Node (CCN) acts as a Media Gateway Controller (MGC). The CCN, such as a Mobile service Switching Center (MSC), Gateway MSC (GMSC), a Transit Switching Center (TSC) or a Media Gateway Control Function (MGCF), selects a Media Gateway (MG) to switch the user plane and to provide in-band equipment if necessary.
In many call cases, multiple CCNs are involved in call setup. Call setup information is signaled between CCNs using call control protocols, such as Integrated Services Digital Network User Part (ISUP), Bearer Independent Call Control (BICC) or Session Initiated Protocol (SIP). When a CCN selects a MG, call control protocols may provide a capability to send the identifier of the selected MG to the succeeding CCN. The succeeding CCN has the choice to select the same MG for user plane switching. In many cases selecting the same MG in subsequent CCN's allows better resource utilization in the nodes and in the network.
A typical call setup scenario for telephone calls (mobile or fixed), utilizes a procedure of forward bearer setup. In this scenario, the bearer is established from the calling side towards the called side. FIG. 1 is a simplified block diagram of forward bearer setup utilizing the BICC call control protocol. A preceding CCN 102 and a succeeding CCN 104 each controls a MG (MG 105 and MG 106 respectively) for user plane switching. In order to achieve forward bearer setup, the succeeding CCN 104 selects a MG first and sends a MG identifier and bearer address information backwards to the preceding CCN 102. The preceding CCN 102 then selects the MG and initiates bearer setup procedure. A mobile station (MS) 120 may operate in, any network (fixed or mobile), but, in this example, a GSM/EDGE Radio Access Network (GERAN) 122 is used. The CCN 102 communicates with the mobile station 120. An MS 124 operates in a GERAN 126 and communicates with the CCN 104. The CCN 102, CCN 104, MS 120, and MS 124 communicate on a signaling plane. The MS 120, MS 124, MG 104, and MS 106 communicate on a user plane.
An Initial Address Message (IAM) message is sent in 130 from CCN 102 to CCN 104 providing call setup information. Next, in 132, the CCN 104 selects the MG 106 and seizes MG resources for the connection end point. An identifier for MG 106 is sent back from CCN 104 to CCN 102 at 134 (e.g., APM (Bearer Control Unit Identifier (BCU-ID)). At 136, the CCN 102 then selects a MG and seizes MG resources for the connection end point. Triggered from CCN 102, MG 105 starts bearer establishment procedures at 138. When Internet Protocol (IP) is used as the user plane transport protocol and BICC is used as the call control protocol, then bearer setup messages are tunneled (not shown) via call control nodes, CCN 102 and CCN 104.
In practice, oftentimes the succeeding node CCN 104 can select from a set of MGs without knowing which MGs can be selected in the preceding node CCN 102. Consequently, there is no guarantee that the MG selected in CCN 104 can also be selected in CCN 102. If CCN 102 and CCN 104 do not select a common MG, longer user plane routes may result.
FIG. 2 is a simplified block diagram of an exemplary existing forward bearer setup utilizing three sites. A network 200 includes a preceding CCN 210 and a succeeding CCN 212. The network includes a MG 214, MG 216, and MG 218. The network includes a MS 222 in GERAN 224. In addition, FIG. 2 illustrates a Public Switched Telephone Network (PSTN) 226. The CCN 210 and MG 214 are located in site 1. The CCN 212 is located in site 2. The MG 216 is located in site 3 and the MG 218 is located in site 4. The MS 222 and CCN 210, CCN 210 and CCN 212, CCN 210 and MG 214, CCN 212 and MG 216, CCN 212 and MG 218, and CCN 212 and the PSTN 226 communicate on a signaling plane. MS 222 communicates with MG 214, MG 216 and MG 218, MG 218 and PSTN 226, and MG 214 and MG 216 communicate on a user plane.
In this example, it is assumed that CCN 212 has to play an announcement, for example due to Intelligent Network (IN) interworking, before the call can be routed to the destination network (e.g., PSTN 226). At the end of the call setup, the MGs on three sides are involved in the call. In GERAN 224, setup message 230 is sent from MS 222 to CCN 210. Next, in 232, CCN 210 sends a BICC IAM message to CCN 212. In 234, CCN 212 determines that an announcement must be played (e.g., due to IN interworking). Next, in 236, CCN 212 selects a MG to establish the bearer (user plane) and to play an announcement. As illustrated, CCN 212 selects MG 216. In 238, CCN 212 sends an identifier of MG 216 backwards to CCN 210. In this example, it is assumed that CCN 210 is unable to select MG 216. Therefore, in 240, CCN 210 selects another MG, in this case, MG 214. In 242, a bearer is established between MG 214 and MG 216 and CCN 210 establishes as well the connection between MS 222 and MG 214 (not shown). In 244, CCN 212 continues call setup after the announcement is played. CCN 212 identifies the call to be routed to PSTN 226. Next, in 246, CCN 212 selects a MG that can connect the user plane to PSTN 226, in this case, the MG 218. Another bearer is then established between MG 216 and MG 218 at 248 and between MG 218 and PSTN 226.
Existing forward bearer setups suffer from the disadvantage of oftentimes utilizing unnecessarily long user plane routes. In addition, extra network resources are utilized for the bearer setup. It would be advantageous to have a bearer setup which conserves network resources while providing a forward bearer setup
The present invention provides a methodology to negotiate MGs between call control nodes that can be used in a call. This negotiation method provides the opportunity for subsequent call control nodes to agree on a common MG node. Such a selection improves the usage of resources in the network.